I changed the throttle body and everything seems to be fine now. Cost me $5 at the local yard! Anyway, things are looking good. Got the idle set and the timing fine-tuned. Nice quiet running engine (I think it did indeed only have 65K on it). I'll try to summarize the entire process with some photos and stuff within a few days...

Now, it's on to other things - rust repair on rear frame, resealing the steering box, new shocks, install stereo, some selective use of bed liner, et.al....

Thanks everyone for the help so far...

96 F250 4x4 Powerstroke
92 F150 4x4 Cummins 4BT Turbodiesel
90 Mitsubishi Mighty Max 4x4 3.0